Association of the Membrane-Penetrating Polypeptide Segment of the Human Erythrocyte MN-Glycoprotein with Phospholipid Bilayers. I. Formation of Freeze-Etch Intramembranous Particles

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RESUMO

The membrane-penetrating segment of the surface MN-glycoprotein of the human erythrocyte is contained intact within the tryptic peptide T(is). We report here on the association of this peptide with hydrated phospholipid vesicles. Under these conditions 80 Å intramembranous particles, as seen by freeze-etch electron microscopy, are produced that are similar in size to those seen in the native erythrocyte membrane. These particles increase in number as a linear function of T(is) concentration and a plot of particle number versus concentration is compatible with a micelle-like phenomenon; from this curve the critical concentration for the formation of particles is estimated to be approximately one mole of T(is) to 120 moles of lecithin. These data suggest that the membrane-penetrating peptide T(is) is being incorporated, monomerically and multimerically, within the hydrocarbon phase of lecithin bilayers.

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